For the business I use Vodafone one net. That gives me a landline and mobile number, but both go straight to the mobile. It's not one of those divert services that costs you to forward the call, just a normal mobile contract but with a geographical landline number as well. So I can have a landline and mobile on the van and stationary which looks better than just a mobile number. Both numbers go to the same voicemail all included in the monthly contract.
It costs £45:00 + VAT a month with the usual unlimited calls, text, data and it comes with whatever top of the line phone you want, I currently have a Sony Experia Z.
It's also useful in that the whole lot is through the company as that's all the lines are used for so there's no bother working out percentages etc. The other benefit is that I know if that phone rings it's work, so I can ignore or answer as I choose.